Control mechanism and method for dual carburetors

ABSTRACT

A throttle valve disposed in the secondary barrel of a dual carburetor is controlled by a diaphragm movable in response to pressures applied on opposite sides thereof. One side of the diaphragm has applied thereto a combined pressure derived from each of the venturis in the primary and secondary barrels of the carburetors. The other side of the diaphragm has applied thereto a combined pressure derived from the primary and secondary barrels at points therein upstream of the venturi with the point in the primary barrel being selected from between the venturi and a choke valve located in said primary barrel. Displacement of the diaphragm caused by pressure imbalances on opposite sides thereof is communicated to the throttle valve in the secondary barrel through a linkage means to control operation of the secondary barrel throttle valve.

United States Patent Kono et a1.

Sept. 2, 1975 [75] Inventors: Tadayoshl Kono; Takao Okuno,

both of Toyota; Mikio Kuno, Aichi, all of Japan [73] Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Tokyo, Japan [22] Filed: June 10, 1974 [21] Appl. No.: 477,974

[30] Foreign Application Priority Data Aug. 11, 1973 Japan 48-93998 [52] US. Cl 261/23 A [51] int. C1. F02M 13/04 [58] Field of Search 261/23 A [56] References Cited UNITED STATES PATENTS 3,013,777 12/1961 White 261/23 A 3,186,691 6/1965 Manning, .lr 261/23 A 3,223,391 12/1965 Shepherd, Jr 261/23 A 3,249,099 5/1966 Saxby 261/23 A Primary Examiner-Tim R. Miles Attorney, Agent, or Firm-Toren, McGeacly and Stanger [5 7] ABSTRACT A throttle valve disposed in the secondary barrel of a dual carburetor is controlled by a diaphragm movable in response to pressures applied on opposite sides thereof. One side of the diaphragm has applied thereto a combined pressure derived from each of the venturis in the primary and secondary barrels of the carburetors. The other side of the diaphragm has applied thereto a combined pressure derived from the primary and secondary barrels at points therein upstream of the venturi with the point in the primary barrel being selected from between the venturi and a choke valve located in said primary barrel. Displacement of the diaphragm caused by pressure imbalances on opposite sides thereof is communicated to the throttle valve in the secondary barrel through a linkage means to control operation of the secondary barrel throttle valve.

3 Claims, 2 Drawing Figures PATENTEBSEP '21'975 FIG.

FIG. 2

CONTROL MECHANISM AND METHOD FOR DUAL CARBURETORS BACKGROUND OF THE INVENTION The present invention relates generally to dual carburetors for internal combustion engines which include an automatic choke unit, and more particularly to a dual carburetor of the type in which a throttle valve in the secondary barrel of the carburetor may be controlled in response to both the opening of the choke valve in the primary carburetor barrel and the operating conditions of the engine.

In conventional dual carburetors, the opening of a throttle valve which is located in the secondary carburetor barrel is controlled by a diaphragm which has applied thereto pressure differences between the pressure at the venturi tubes of the primary and secondary carburetor barrels and the pressure downstream of a choke valve located in the primary carburetor barrel. The choke valve is so arranged that it will be automatically controlled in response to movement of a bimetal' lic spring member or the like, depending upon the operating conditions of the engine. As a result, the choke valve will be closed before the engine is sufficiently warmed up and the pressures acting upon the diaphragm will become equal to each other so that the diaphragm will not undergo displacement before sufficient engine warming is achieved thereby holding the throttle valve in the secondary carburetor barrel closed.

As a result, sufficient air will not be supplied to the combustion chambers of the engine from the carburetor immediately after the engine is started during extremely low temperature conditions or when the vehi cle is being operated at high elevations, and there re sults supply of a rich fuel-air mixture. Because of this, the engine will be unable to produce sufficient power to operate the vehicle and engine stalling may occur.

In some conventional dual carburetors, there is provided a diaphragm which controls the opening of the throttle valve located in the secondary carburetor barrel, with the diaphragm being actuated in response to pressure differences between atmospheric pressure and the pressure at the venturis in the primary and secondary carburetor barrels. However, such systems involve significant defects in that the throttle valve in the secondary carburetor barrel will be opened or closed only in response to the pressures at the venturi tubes and independently of the level of opening of the choke valve in the primary carburetor barrel. Therefore, excessive amounts of air will be charged into the combustion chambers of the engine during a time when a rich fuelair mixture should be supplied. Thus, a lean fuel-air mixture will be supplied into the combustion chamber of the engine and, again, insufficient engine power will be developed.

Furthermore, in conventional dual carburetors of the type incorporating a reloader for controlling the opening of the throttle valve in the secondary carburetor barrel, it has been found that a distinct disadvantage of such carburetors arises as a result of the complexity of their construction.

Accordingly, the present invention is intended to provide a dual carburetor of the type in which the opening of the throttle valve located in the secondary carburetor barrel may be controlled in an optimum manner under any operating condition of the internal combustion engine to which the carburetor is applied.

SUMMARY OF THE INVENTION Briefly stated, the present invention may be described as a control system for a dual carburetor having a primary barrel including first venturi means and a first throttle valve located on one side thereof, a secondary barrel including second venturi means and a second throttle valve located on one side thereof, and a choke valve located in the primary barrel on the side of said first venturi means opposite said first throttle valve. A movable diaphragm is mounted to divide a diaphragm chamber into a pair of pressure chambers with one of said pressure chambers being communicated with ports opening into the passages of the primary and secondary carburetor barrels, said ports being equivalently spaced, respectively, from said first and second venturis, with the port opening into the primary barrel being located downstream of the choke valve between the choke valve and the first venturi. The other pressure chamber is communicated with ports opening directly into the venturi sections of both carburetor barrels. As a result, the opening of the throttle valve in the secondary carburetor barrel may be controlled in re sponse to movement of the diaphgram which is con nected to said second throttle valve by a linkage mechanism.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a schematic diagram of an engine having a dual carburetor constructed in accordance with the present invention; and

FIG. 2 is a schematic sectional view of the dual earburetor shown in FIG. 1 incorporating the features of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, there is shown a dual carburetor 1 comprising a primary barrel 2 and a secondary barrel 3. Air is introduced into the air intake section of the carburetor through an air cleaner 4 with an intake manifold 5 operating to deliver air-fuel mix 1 ture to the combustion chamber 6 of an internal com bustion engine. The primary carburetor barrel 2 includes a choke valve 8 which is automatically opened and closed by a bimetallic spring member 7. The choke valve 8 is located within the primary barrel 2 on one side of a large venturi tube 9 and a throttle valve 10 located on the opposite side of the venturi tube 9 is operatively coupled to an accelerator pedal (not shown). A small venturi tube 11 is disposed within the large venturi 9 and a nozzle 14 extends into the small venturi 11 from a float chamber 12 through a passage 13.

The secondary carburetor barrel 3 also includes a large venturi 9', a small venturi 11, a nozzle 14', and

relationship relative to those of the primary carburetor barrel 2. A shaft of the throttle valve 10 of the secondary carburetor barrel 3 is operatively coupled by a linkage mechanism 18 to a diaphragm 17 which is disposed within a casing 16. The opening of the throttle valve 10' is controlled in response to movement of the diaphragm 17 through operation of the linkage mechanism 18.

The casing 16 is divided by the diaphragm 17 into a pair of pressure chambers 19 and 20, with the pressure chamber 19, located to the left in FIG. 2, being communicated with a pressure intake port 21 opening into the primary carburetor barrel 3 at a point downstream of the closed choke valve 8. A tube 23 having inserted therein a nozzle or orifice 22 extends between the port 21 and the chamber 19.

In a similar manner, a pressure intake port 21' opening into the secondary carburetor barrel 3 at a position corresponding to the position of the pressure intake port 21 of the primary carburetor barrel 2, is communicated with the pressure chamber 19 through a tube 25 including a nozzle orifice 24 and through the tube 23.

The coefficients of the nozzle orifices 22 and 23 are so selected that a desired pressure difference may be produced between the two pressure chambers 19 and 20. That is, the pressure transmitted to the pressure chamber 19 is such that it represents a balance between the pressures at the pressure intake ports 21 and 21.

Pressure chamber 20, shown to the right in FIG. 2, is communicated through a tube 28 with a passage 27 which, in turn, is communicated with ports 26 and 26 opening at the large venturis 9 and 9', respectively.

In the operation of the dual carburetor of the present invention, when the engine has not yet achieved a sufficiently warm condition, the bimetallic spring 7 will not undergo movement and the choke valve 8 is almost closed thereby providing only a small opening in the choke section. When engine load is small under the aforementioned condition, i.e., when the opening of the throttle valve 10 is small, the negative pressure developed at the large venturi 9 in the primary carburetor barrel 2 is low. Therefore, the balanced pressure between this negative pressure and the atmospheric pressure existing at the large venturi 9 in the secondary carburetor barrel 3 will be transmitted through the openings 26 and 26, the passage 27 and the conduit 28 to the right pressure chamber 20. The balanced pressure obtained between the pressures at the ports 21 and 21 is almost equal to atmospheric pressure and it is applied to the left pressure chamber 19. Therefore, the pressure difference between the two pressure chambers 19 and will be low and, therefore, the diaphragm 27 will not be displaced. As a result, the throttle valve 10 in the secondary carburetor barrel 3 will be held in its closed position.

As engine load is increased and the opening of the throttle valve 10 in the primary carburetor barrel 2 is increased, negative pressure produced through the large venturi 9 will be increased. This negative pressure balanced with the pressure at the large venturi tube 9 in the secondary carburetor barrel 3 will be transmitted to the right pressure chamber 20 through the ports 26 and 26, the passage 27 and the conduit 28. Since the pressure in the right pressure chamber 20 will be lower than that in the left pressure chamber 19, the diaphragm 17 will be displaced to the right, as seen in FIG. 2, and, as a result, the shaft of the throttle valve 10' will be rotated through operation of the linkage mechanism 18 so that throttlesvalve 10 will be opened. As a result, a rich fuel-air mixture will be supplied from the primary carburetor barrel 2 to the combustion chamber 6 while a lean fuel-air mixture will'be supplied to the combustion chamber 6 from the secondary carburetor barrel 3. Thus, sufficient fuel and air will be supplied to the combustion chamber 6 of the engine thereby resulting in an increase in engine output.

When the engine is sufficiently warmed up, the bimetallic spring 7 will be heated and, accordingly, the choke valve 8 will be opened. The negative pressure at the opening 26 of the primary carburetor barrel 2 will be higher than at the opening 21. The balanced pressure will be transmitted to the right pressure chamber 20 through the ports 26 and 26, the passage 27 and the conduit 28. Since the negative pressure in the right pressure chamber 20 will be higher than that in the left pressure chamber 19, the diaphragm 17 will be displaced to the right, as seen in FIG. 2, thereby causing the throttle valve 10' to open through operation of the linkage mechanism 18 connected to the shaft 15. Accordingly, sufficient fuel and air will again be supplied to the combustion chamber 6 of the engine.

As described hereinbefore, as a result of the operation of the present invention, the throttle valve in the second carburetor barrel may be opened, even when the choke'valve is closed, depending upon the operating conditions of the engine so that a fuel-air mixture having an optimum air-fuel ratio may be delivered into the combustion chamber of the engine despite any changes in the operating conditions of the engine. Therefore, undesireable decrease in engine output may be prevented. Furthermore, there is eliminated the need for a reloader for controlling the opening of the throttle valve in the secondary carburetor barrel and, as a result, the construction of the dual carburetor is, in accordance with the present invention, greatly simplified and improved.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be under stood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. In a dualcarburetor having a primary barrel including first venturi means and a first throttle valve located on one side thereof, a secondary barrel including second venturi means and a second throttle valve located on one side thereof, and a choke valve located in said primary barrel on the side of said first venturi means opposite said first throttle valve, a control mechanism for said second throttle valve comprising a diaphragm chamber having a diaphragm therein dividing said diaphragm chamber into a pair of pressure chambers, said diaphragm being displaceable in response to pressure differences between said chambers, linkage means interconnecting said diaphragm with said second throttle valve for movement thereof in response to displacement of said diaphragm. first conduit means for applying to one of said pressure chambers the pressures within both said first and said second venturi means, and second conduit means for applying to the other of said pressure chambers pressures from both said primary and secondary barrels taken at points therein substantially equivalently spaced from said first and second venturi means on the sides thereof, respectively,

opposite said throttle valves, said point in said primary barrel being located between said choke valve and said first venturi means.

2. A control mechanism according to claim 1 wherein said second conduit means comprise a pair of conduits each extending, respectively, between said points in said primary and secondary barrels and said other pressure chamber, said control mecanism further including first and second nozzle means located, respectively, in each of said pair of conduits.

3. A method for operating a dual carburetor having a primary barrel including first venturi means and a first throttle valve located on one side thereof, a second barrel including second venturi means and a second throttle valve located on one side thereof, and a choke valve located in said primary barrel on a side of said first venturi means opposite said first throttle valve,

said method comprising the steps of combining pressures taken respectively from within said first and said second venturi means to derive therefrom a first combined control pressure, combining pressures taken respectively from points from within said primary and secondary barrels, said points being substantially equivalently spaced from said first and said second venturi means on a side of each of said venturi means opposite said throttle valves to derive therefrom a second combined control pressure, said point within said primary barrel being selected from between said choke valve and said first venturi means, and applying said first and said second combined control pressures to control operation of said second throttle valve in accordance with differences between said control pressures. 

1. IN A DUAL CARBURETOR HAVING A PRIMARY BARREL INCLUDING FIRST VENTURI MEANS AND A FIRST THROTTLE VALVE LOCATED ON ONE SIDE THEREOF, A SECONDARY BARREL INCLUDING SECOND VENTURI MEANS AND A SECOND THROTTLE VALVE LOCATED ON ONE SIDE THEREOF, AND A CHOKE VALVE LOCATED IN SAID PRIMARY BARREL ON THE SIDE OF SAID FIRST VENTURI MEANS OPPOSITE SAID FIRST THROTTLE VALVE, A CONTROL MECHANISM FOR SAID THROTTLE VALVE COMPRISING A DIAPHRAGM CHAMBER HAVING A DIAPHRAGM THEREIN DIVIDING SAID DIAPHRAGM CHAMBER INTO A PAIR OF PRESSURE CHAMBERS, SAID DIAPHRAGM BEING DISPLACEMENT IN RESPONSE TO PRESSURE DIFFERENCES BTWEEN SAID CHAMBERS, LINKAGE MEANS INTERCONNECTING SAID DIAPHRAGM WITH SAID SECOND THROTTLE VALVE FOR MOVEMENT THEREOF IN RESPONSE TO DISPLACEMENT OF SAID DIAPHRAGM, FIRST CONDUIT MEANS FOR APPLYING TO ONE OF SAID PRESSURE CHAMBERS THE PRESSURES WITHIN BOTH SAID FIRST AND SECOND VENTURI MEANS, AND SECOND CONDUIT MEANS FOR APPLYING TO THE OTHER OF SAID PRESSURE CHAMBERS PRESSURES FROM BOTH SAID PRIMARY AND
 2. A control mechanism according to claim 1 wherein said second conduit means comprise a pair of conduits each extending, respectively, between said points in said primary and secondary barrels and said other pressure chamber, said control mecanism further including first and second nozzle means located, respectively, in each of said pair of conduits.
 3. A method for operating a dual carburetor having a primary barrel including first venturi means and a first throttle valve located on one side thereof, a second barrel including second venturi means and a second throttle valve located on one side thereof, and a choke valve located in said primary barrel on a side of said first venturi means opposite said first throttle valve, said method comprising the steps of combining pressures taken respectively from within said first and said second venturi means to derive therefrom a first combined control pressure, combining pressures taken respectively from points from within said primary and secondary barrels, said points being substantially equivalently spaced from said first and said second venturi means on a side of each of said venturi means opposite said throttle valves to derive therefrom a second combined control pressure, said point within said primary barrel being selected from between said choke valve and said first venturi means, and applying said first and said second combined control pressures to control operation of said second throttle valve in accordance with differences between said control pressures. 